Earth-bound navigation mostly relies on local, terrestrial cues - like landmarks, the geomagnetic field, smells, sounds and so on. But, as we’ve seen, many animals - including us humans - also make use of the sun, moon and stars.

The history of human celestial navigation (the subject of my book, Sextant) is the story of how astronomers, mathematicians and instrument-makers down the centuries gradually improved the accuracy with which we could predict and measure the positions of heavenly bodies.

By the mid-eighteenth century their combined efforts meant that it was at last possible to determine a ship’s position on the open ocean using these techniques - to within a few miles (in good conditions).

But what if you’re trying to track the position of a space vehicle travelling at great speed across the Solar System or even beyond?

You can fix your position in space by reference to the stars - just as you can on the surface of the earth - but there is a problem.

Many of the brightest stars are close neighbours (cosmically speaking) and, though they may appear to be stationary, they actually move in complicated ways. If you want to navigate really accurately you have to factor in their motion, but that’s difficult unless you have a stable frame of reference against which to measure it.

So what you need is a set of heavenly bodies so extremely distant that they really don’t move at all.

Enter quasars. These extraordinary objects are among the most powerful sources of energy in the whole universe, and are almost certainly supermassive black holes at the hearts of other galaxies.

A single quasar can generate as much energy as the entire Milky Way - which consists of hundreds of billions of stars. In fact they are so powerful that astronomers can detect them even when they are tens of billions of light years away - on the far side of our expanding universe.

Quasars then offer the perfect solution to this navigational problem.

A new set of observations from a star-mapping satellite called Gaia now includes 1.6 million quasars, as well as a billion stars that are much, much closer to us. The quasars enable astronomers to determine with exquisite precision the velocities of the nearer stars on which super-accurate navigational calculations can then be based. (Here’s a link to a mesmerising animation showing the complex patterns of ‘proper motion’ displayed by stars in the Milky Way - based on on observations from Gaia.)

The Gaia observations furnish the most accurate celestial frame of reference yet devised.

In addition to enabling accurate deep space navigation, the Gaia observations also play a valuable role in improving the accuracy of earthbound satellite navigation systems - like GPS.

If you want to know more, read this excellent recent article in the journal Science by Joshua Sokol.